Automatic stoker



April 16, 1940. F', '5 2,197,428

AUTOMATIC STOKER Filed June 11, 1337 4 Sheets-Sheet 1 INVEN TOR.Clarence E Erb ATTORNEY.

April 16,1940. c. F ERB AUTOMATIC STOKER 4 Sheets-Sheet 2 u u u u a o aa c u DUE:

Filed June 11,

san 5::

INVENTOR. Clarence F Erb AORNEK April 16, 1940. c. F. ERB

AUTDIATIC STOKER Filed' June 11, 19s":

4 Sheets-Sheet 3 INVENTOR Clarence F Erb 16, 1940. c. F. ERB 2,197,428

AUTOMATIC STOKER Filed June 11, 1937 4 Sheets-Sheet 4 Q Eszllllllllllllllllllll 1 g x A g a INVENTOR. Clarence EErb BY 1 a i 1 ZTTORNEZ.

Patented Apr. 16, 1940 UNITED STATES PATENT OFFICE AUTOMATIC STOKERstokers and more particularly to stokers of the type utilizingreciprocating devices which move 1 the fuel from the front to the rearof the furnace and supply primary air for combustion. Broadly stated,the objects sought to be accomplished by this invention are thesimplification and economy of construction and maintenance of theconstituent elements, flexibility of control, and highly eflicientcombustion of the fuel. To carry out these objects, the inventionincludes innovations in the design of the oscillating fuel feedingelements, commonly termed "stoker bars" and in the supporting meanstherefor, together with an improved apparatus for operating the fuelfeeding bars.

Heretofore, in automatic stokers of the general type underconsideration, the practice has been to form the entire fuel bedsupporting surface of adjacent oscillating stoker bars which practiceresults in theuse of a large number of elements and a consequent highcost of the installation. Moreover, the tendency of the contiguous barsto warp in use causes them to wedge one against the other, thusinterfering with the normal operation of the stoker.

Therefore, the primary object of this invention is to provide anautomatic stoker of the type utilizing stoker bars in. which arelatively small number of such bars are used, whereby the initial costof the installation is reduced and the liability of the system tofailure is minimized.

Another object of the invention is to provide an improved support forthe stoker bars, which support will not burn out in use and whichpreheats the primary air for combustion.

A further object of the invention is to provide an improved stoker barwhich maintains the fuel bed in better condition for more efficientcombustion.

A further object of the invention is to provide improved means foroperating the stoker bars whereby the system is rendered more flexibleand dependable in use. a

A still further object of the invention is to provide improved means foroperating the stoker bars whereby the stoker remains at least partiallyoperative even though some obstruction prevents the normal movement ofone of the bars.

The construction of the operating mechanism is such that no damageresults from the jamming of any movable parts of the stoker itself, thisbeing achieved without the use of shear pin couplings or other frangibleelements which must be replaced by expert workmen to render the stokeragain operable.

These and other objects and advantages of the invention will becomeapparent from a consideration of the drawings and the following detailedspecification.

In the drawings:

Figure 1 is a cross-sectional view of a stoker installation constructedin accordance with my invention;

Figure 2 is a top view of the stoker bars, showing their relation toother elements of the furnace and stoker;

Figure 3 is an end view of the stoker;

Figure 4 is a partial cross-sectional view taken along the line 44 ofFigure l; and

Figure 5 is a diagrammatic view of the stoker actuating mechanism, partsthereof being shown in section. V

The stoker is illustrated as applied to a boiler furnace of conventionaldesign having a masonry foundation'lll, a front wall l1, water tubes I lconnecting with the header l2, and a transverse baflle wall IS. A hopperI 4 having a flat bottom wall is afllxed to the front of the boiler andthe stoker bars 25 of my invention are adapted to propel solid fuel fromthe hopper to the fuel bed within the furnace.

To support the fuel bed and the stoker bars I provide a flat hollowbox-like structure 20, horizontally disposed, and extending the entirewidth of the furnace, which may be conveniently made by castingintegrally the top and side walls and welding or otherwise securingthereto a metal plate or sheet to form the bottom wall. As shown inFigure l, the support 20 extends outwardly a considerable distance fromthe front wall I! of the furnace and thus aids in supporting the hopperl4. To the front wall of the support 20 there is secured thehorizontally disposed hydraulic cylinders 40 and 60 which are providedwith the pistons 4| and it connected with the rods 32 and 62,respectively,-which extend within the support and connect with thestoker bars 25.

As shown, the stoker bars 25 are slidably mounted on the upper surfaceof the support 20, suitable guides 3' being provided to insure .themaintenance of proper position, and are two in number although it shouldbe understood that any number may be used, depending on the width of thefurnace and other specific conditions. The bars 25 each consists of ahollow metal body open on the bottom and having on its top wall amultiplicity of upstanding lugs 34 and a multiplicity of adjacent airdelivery orifices of comparatively small size. The longitudinalcross-section of the bar 25 in Figure 1 shows a horizontal porthe inwardmovement of the bar. .10

tion 35 adjacent the furnace wall I1 and a humped portion 21 adjacentthe rear end of the bar. Integral with the bar 25 is the wedge-shapedmember 29 positioned within the hopper and being provided with avertically extending shoulder 36 to move the fuel into the furnace. uponThe wall ll of the furnace is provided with the openings 88 throughwhich the bars 25 extend. The upper wall of the support 20 is providedwith a pair of openings 2| and 22 for each bar which openings providemeans for the conduct of air from within the support 20 to within thebars. Tl'he front opening 22 also allows passage of the bracket which isrigidly attached to the bar 25 at its upper end and to the rod 32 or 62at its lower end by means of the link 3|. It is thus apparent thatoscillation of the pistons 4| or 6| within the cylinders 40 or 80results in oscillating movement of the connected bar 25.

To provide primary air for combustion, I provide the blower 42 driven bymotor 44, the blower discharging into the hollow support 20 through theduct 33. Since the support 20 is air tight except for the openings 2|and 22 it follows that the air coming into it will pass through the saidopenings, into the hollow grate bars 25 and through the orifices thereofto the fuel bed. Since the hollow support 20 underlies the entire fuelbed, a considerable volume of turbulent air is always present whichprevents the buming of the upper wall of the support. Moreover, the airpassing through the support 20 is heated before it reaches the fuel bed,thus increasing the efficiency of the combustion. If desired, downwardlyextending radiating fins may be attached to the upper wall of thesupport 20 to further the cooling of the upper wall and the preheatingof the air.

Each opening 88 in the front wall I! of the furnace is provided with agate 83 slidably mounted for vertical movement on the outer surface ofthe wall I! in the guides 81. Gates 83 are operated by the verticallypositioned cylinders 80 and I 00 secured to the outer surface of thewall I! above the gates. Pistons 8| and IN within the cylinders are eachprovided with a downwardly extending rod 82 and I02 the lower ends ofwhich pass through apertures in lugs 84 rigidly attached to the gates83. Each of the rods 82 and I02 have a cotter pin passed through theirlower end below -the lug 84 and a second pin passed through at a pointspaced from the upper surface of the lug 84. A washer 86 abuts againstthe second mentioned pin and a strong helical spring 85, encircling therod, is positioned between the washer and the upper end of the lug. Thearrangement is such that upward movement of the rod results in thepositive upward movement of thegate whereas downward movement of the rodresults in a spring pressed movement of the gate. If some obstructionprevents the downward movement of the" gate, the rod can continue itsmovement,

the spring 85 taking up the necessaryrelative movement between the partsbut continuing to 20 terminates short of the wall I3 allowing space I9therebetween for an ash and clinker drop. The pen 24 may be of anydesired construction, it may be provided with orifices or slots, it mayreceive air beneath from the box 20, and a portion thereof may overliethe drop I8. Suitable doors I5 are provided in the side walls of thefurnace above the grate bars 25 and an ash cleanout door I5 may beprovided below the support 20.

Figure 5 illustrates the operating and control system as applied to astoker installation utilizing two stoker bars and two gates as describedin connection with Figures 1 to 4, inclusive. Rod 32 connected withpistons 4| of cylinder 40 operates the upper bar of Figure 2 and rod 82connected with piston SI of cylinder operates the lower bar of Figure 2.Rod 82 connected with 8| of cylinder 80 actuates the left gate 83 ofFigure 3 which controls the opening about the stoker bar 25 operated bypiston 4|. Rod I02 connected with piston IOI of cylinder I00 operatesthe other of the gates 83. Cylinders 80 and I 00 are identical andcylinders 40 and 80 are identical in construction.

Pistons 4|, 5|, 8| and IN are hydraulically operated and to supply aquantity of fluid under pressure, I provide the pump I54 having an inletI55, an outlet I56 and being driven through shaft I53 by the variablespeed motor I50. A source of electrical power I5I is provided for motorI50 and a variable resistance I52 is interposed between the power sourceand the motor so that the speed of the motor and the rate of flow offluid from the pump may be readily controlled. The change-over valvegenerally indicated at I20 is provided to reverse the flow of the fluidto the cylinders 40, 50, 80 and I00 to effect the oscillating movementof the stoker bars and gates and consists generally of a cylinder I 2|having therein a piston I24 and an integrally attached valve housing I22 having a valve I34 therein actuated by the piston I24. A rod I25 isrigidly attached atone end of the piston I24 and extends outwardlythrough the end wall of the cylinder |2I and into the housing I22. Eachend of the cylinder I2I is provided with a port for a purpose to belater described. The lower wall of the valve housing I 22 is providedwith three longitudinally spaced ports to which are connected tubes 9|,I51 and I2, respectively, and the end wall of the housing is providedwith a port to which is connected the pump outlet tube I56.

Longitudinally slidable on the inner surface of the bottom wall of thehousing I22 is the valve I34 which is providedwith an arched recess I35in its bottom wall to bridge two of the three spaced ports and alongitudinal slot (not shown) on its upper surfac to receive a portionof the rod I25. The upper surface of the valve I34 is further milled toprovide shoulders engaged by the spaced collars I26 and |3| rigidlyfastened in any suitable manner to the rod I25. Another collar I 30spaced from the middle collar I3| is rigidly attached to the end of therod I25 opposite the piston I24. A block I32 having a longitudinallyextending bore I33 and being provided with a grooved and milled uppersurface similar to that of the valve I34 is positioned between thecollars I30 and |3I and between the intervening portion of the rod I25and the upper surface of the bottom wall of the housing I 22. As shownthe block I32 is spaced from valve I34 to allow the port I2 to receive75 fluid from within housing I22 when'the parts are in the positionshown.

Formed integrally with or suitably attached to the upper surface of therod I2l-between the collars I" and iii is the tooth I having inclinedsurfaces as shown whichare adapted to be traversed by the complementaryinclined surfaces of the wedge I38. The wedge III is carried by theshank I81 which is spring-pressed downwardly by the helical spring I29housed within the cos-'- ing I2I fastened to the upper wall of the valvehousing I 22. The washer I39 secured to the shank I31 transmits theforce to the shank and confines the spring. In order that the downwardforce exerted on the wedge I may be varied, a

screw I28 is in screw threaded engagement with the upper wall of thehousing I21 and engages a washer Ill overlying the top of spring I21.Rotation of screw I2l alters the compression of the spring and the forceexerted on the shank III.

longitudinal movement of the rod I25 causes the contacting inclinedsurface of the wedge I" toride up the inclined surface of the tooth Iagainst the expansive force of the spring. Consequently the forcerequired to move the rod is determined by the expansive force exerted bythe spring. When the tip of the wedge I38 passes the high point of thetooth I", the spring, acting through the inclined surfaces, will aid thefurther movement of the rod thus giving a snap action to the movement ofthe parts. a The block I supports the end of the rod I2! against theforce of the spring I29 and is moved along with the rod by the collarsI3. and Iii. Likewise, the valve I is held against the inner surface ofthe bottom wall of the housing I22 by the rod I25 and spring I2! and ismoved along with the rod I25 by the collars I2! and iii. In the positionof the ports, as illustrated, port ii is connected with port Ii'l by therecess I which does not connect with the general space within housingI22. When the piston I24, valve I" and block I are moved to the right oftheir strokes,

' port I" is connected with port I2 and port ii control the supply offluid under pressure to the cylinders II and C0. The valves l9, It, 90and Ill are one-way valves, allowing fluid to flow through them only inthe direction of the arrows.

Assume the systemof Figure 5 applied to a stoker installation, viewedfrom the front, with the cylinders in their proper relative positions.The left stoker bar is in its outward position and the left gate is inits lower position closing oi! the opening 88 above the bar. The rightstoker bar is in its inward position and the upper position of pistonIIII indicates that the gate above this bar is up. Now, in order thatthe left bar mayfeedfuelitisnecessarytoflrstraisethe left gate and inorder that-the right bar may not withdraw live coals'from the furnace,the right gate should be lowered before the bar begins its outwardmovement.- This sequence is brought about by the following means. Fluidcoming from the pump I" reaches casing I22 through tube II! and enterstube I2 from intotubesllandll. Thefluid into ii and acts against pistonsame and consequently the left gate. II reaches the upper end of itstravel, port it uncovered and the fluid under pressure flows throughtube 41 and acts against the outer end of piston 4| to move the pistonand the left stoker bar inwardly'to feed a charge of fuel to the bed. Atthe same time the fluidin branch tube II passes through tube I08 andmoves piston IOI downwardly thus closing the right gate and uncoveringport Ill. This enables fluid to reach.

the cylinder u and move the stoker bar outwardly.

As piston OI moves upwardly the fluid above it (not under pressure) isdischarged through tubes 'I'I, 9i, recess I35, and tube III to thereservoir I". As piston ll moves inwardly, fluid in the inner end of thecylinder ll discharges piston II and right through tube ll, check valve9., tubes II, 11, ll,

fluid is admitted to-the stoker bar cylinders l0 and ll. If someobstruction prevents the down-' ward movement of the gate, its pistoncontinues its travel, the relative movement being taken up by .thespring 02. Upon removal of the obstruction, by the inward movement ofthe stoker bar, for example, thespring II will close the gate.

Normally all pistons will reach the end of their strokes and furtherfluid coming into the dis-- tribution system through'tube 12 will tendto flow through the tube I2. Pressure will build up within the systemand an increasing force will be exerted on the head of piston I 24. Whenthis force overcomes the force of spring I20 acting through the inclinedsurfaces of wedge I" and tooth I36, the piston will move to the rightwith a snap action, moving valve I" to the right whereby the recess I35will bridge ports I" and W2 and the port 9i will be open to the generalspace within the housing I22 so that it may receive fluid coming intoI22 through tube I". Since tube 52 is-always connected with port I2, thepiston I24 will be moved to the right if suflicient pressure isreached,irrespective of the position of the pistons ll and I. Therefore, even ifthe movement of the stoker bars is obstructed, the reversing valve willoperate. and cause the bars to move in opposite directions. Theadvantages of this feature should be obvious. In many instances thereversal of movement will free the bar or removetheobstruction, allowingthe stoker to continue its normal operation.

No attention is rcquired. Also it should be noted that if one of thebars becomes immovably jammed, the other bar will continue its normaloperation, thus maintaining the flre.

Upon shifting of the valve III to the right, fluid passes from the pumpI through tube I" and easing I22'into tube ll where it branches intotubes II and II. From tube II, the'fluid flows against piston 8i, movingit down, through tubes II, I4 and into cylinder 40, moving piston II andthe left stoker bar outwardly. From tube II, the fluid flows intocylinder Ill, moving piston Ill upwardly; through tube and into cylinder50, moving piston BI and the right stoker bar inwardly. As piston 8|moves downwardly, fluid below it discharges through tubes H, 13, 12,recess I35 and tube I51 to the reservoir I60. Fluid in front of piston4I discharges through tube 41, check valve 49, tubes 50, 13, 12, recessI35 and tube I51 to I60. Fluid above piston IOI moves through tubes I03,1|, 12, recess I05 and tube I51 to I60. Fluid in the rear portion ofcylinder GI discharges through tube I05; check valve I04, tubes I03, 1|,12, recess I35 and tube I51 to reservoir I50. When the pistons all reachthe ends of their strokes or when for other reasons no more expansion ofthe spaces takes place, pressure builds up in lines 9i and 90, exertingan increasing force on the right end of piston I24, moving the piston tothe left against the force exerted by the spring I 29, thus operatingthe reversing valve to cause the gates and bars to move in reversedirections. If desired, a pressure relief valve may be coupled betweentubes I 55 and I55 to prevent injury to the system because of excessivepressures.

In operation, the change-over device I20 is adjusted to operate at apressure approximately twice that required for the normal operation ofpistons 4|, 6|, 8| and II. For example, if a pressure of 40 lbs. persquare inch is found to be suflicient for the normal operation of theabove mentioned pistons, the screw I28 is so set that a pressure of 80lbs. per square inch is required to move piston;I24 to the other end ofits stroke. This arrangement insures the full operation of the stokerbars, if unobstructed, before their direction of travel is reversed. Thespeed of operation of the stoker is determined by the rate of flow offluid from the pump I54 which rate may be controlled by manipulation ofthe rheostat I52. If desired, rheostat I52 may be automaticallycontrolled by any of the known stoker control devices.

During the outward movement of the stoker bar 25, the wedge-shaped end29 thereof passes under the fuel in hopper I4, stirring up the fuel andcausing a quantity thereof to move over the high point of the wedge andfall on the bar thus insuring that some fuel will be fed with eachinward movement of the bar. As the bar begins its outward movement thebed of coals will be squeezed between the gate 83 or wall I1 and theraised portion 21 of the bar which action will break up any incrustationwhich has begun, thus effectively preventing the formation of clinkers.At the same time some of the bed will be forced about, and over theraised portion 21 where it will receive an increased supply of air topromote the thorough burning of the fuel. Before reaching the ash dropI9, unburnt particles of the fuel must traverse the inclined pan 24through a region of high temperature, thus insuring the completecombustion of the fuel. Since the bars 25 operate in opposite directionsat any one time, the entire fuel bed is periodically agitated. It canreadily be seen, however, that the fuel on the bars adjacent the wall I1is less disturbed than the fuel which has progressed to the raisedportions 21. The fuel is at least p rtially coked before it reaches theraised portion 21.

The above specifically described embodiment of my invention should beconsidered as illustrative only. It is obvious that the basic conceptsof my invention may be carried out by apparatus other than thatdescribed and that the stoker would be still operative without the useof the gates 03 and their accompanying operating mechanisms.

Having thus described my invention, what I claim is:

1. In an automatic stoker, a hollow oscillating grate bar having sideand top walls and an open bottom, said top wall having a raised portionadjacent one end of said bar, a wedge shaped member attached to theother end of said bar, said member being provided with a shoulderwhereby fuel may be propelled along said bar towards said raised portionupon oscillation of said bar.

2. A device according to claim 1 further characterized by a multiplicityof upstanding lugs on said top wall.

3. A device according to claim 1 further characterized by a multiplicityof apertures in said top wall.

4. A stoker installation comprising a hollow closed support, a hollowgrate bar slidably mounted on said support, apertures in said grate bar,a shoulder adjacent one end of said bar, a fuel hopper supported on saidhollow su'pport and encasing said shoulder, means to conduct air intosaid hollow support, means to conduct air nace, a grate bar slidablymounted on said support and having a portion extending through anaperture in the wall, an upstanding shoulder on said bar on the portionoutside said wall, said aperture extending above said bar, a fuel hopperoutside said wall encasing the shouldered end of said bar, and a gateslidably mounted on said wall and adapted to close that portion of theaperture extending about said grate bar.

6. A stoker installation comprising a furnace having a front wall, anaperture in said wall, a support within said furnace, a perforated gratebar slidably mounted on said support and having a portion extendingthrough the aperture, an upstanding shoulder on said bar on the portionoutside said wall, said aperture extending above said bar, a fuel hopperoutside said wall encasing the shouldered end of said bar, a gateslidably mounted onsaid wall and adapted to close that portion of theaperture extending above said grate bar, and means to first move saidgate and thereafter move said grate bar.

7. A stoker installation comprising a hollow closed support, a hollowperforated bar slidably mounted on said support, a shoulder on said baradjacent one end thereof, a fuel hopper about said shouldered end, meansto conduct air into said support, means to conduct air from said supportinto said bar, a cylinder mounted on said support, a piston in saidcylinder connected with said bar, and means to supply operating fluid tosaid cylinder. "L r 8. A stoker installation comprising an oscillatingstoker bar, a hopper, a portion of said bar extending into said hopper,an aperture in said hopper through which said bar extends, said apertureextending above said bar, a gate slidably mounted 'on the wall of saidhopper adapted to close said extended portion of the aperture, a closedcylinder having a port at either end and a I port in its side wall,apiston within said cylinder connected with said gate, fluid pressuremeans to operate said bar, a tube connecting said second connected withsaid fluid supplying means opermentioned port with said fluid pressuremeans. said piston when in one position closing said second mentionedport, means to supply fluid imder pressure to one of said flrstmentioned ports, the arrangement being such that the piston must firstbe moved a predetermined distance before fluid can flow through thesecond mentioned port and the tube into the said fluid pressure means.

9. Apparatus for the sequential operation of oscillating elementscomprising fluid pressure motors connected with said elements, means tosupply fluid under pressure to said motors, means controlled by theactuation of one of said motors in control of the flow of fluid to theother of said motors, and a pressure responsive element able to reversethe direction of flow of the flui through said motors. I

10. A stoker installation for a furnace comprising .a hollow closedsupport having a horizontally disposed upper surface extending throughthe front wall of the furnace, a plate inclined toward the rear of thefurnace and mounted on the rear portion of said support, a hollow gratebar havins side'and top walls and an open bottom slidably mounted onsaid support forwardly of said plate,

said top wall being apertured and having a raised portion adjacent theend nearest the plate, said top 'wall sloping downwardly from the top ofsaid raised portion toward said plate, a fuel hopper above the outer endof saidsupport, means to longitudinally oscillate said grate bar, meanson said bar to propel fuel from said hopper toward said raised portionupon oscillation thereof,

means to supply air-to within said support, and means .to conduct airfrom said support to said grate bar.

11. A stoker installation for a furnace comprising a hollow closedsupport having a horizontally disposed upper surface extending throughthe front wall of the furnace, a hollow grate bar having side and topwalls and an open bottom slidably mounted on said support, said top wallbeing apertured and having a raised portion adjacent the one endthereof, said top wall sloping downwardly from the top of said raisedportion to the end of said bar, the other end of said bar being wedgeshaped and having an upwardly extending shoulder, a fuel hoppersupported on the outwardly extending end of said support and encasingsaid shoulder, means to supply air to within said support, means toconduct air from said support to said grate bar, and means to oscillatesaid grate bar longitudinally.

12. A stoker installation for a furnace having a front wall comprisingzahollow closed support having a horizontally disposed upper surfaceextending through the front wall of the furnace, a fuel hopper supportedon the outwardly extend- & ing end of said support, a hollow grate barslidably mounted on said support, apertures in said grate bars,a'shoulder adjacent the outer end of said bar within said hopper, meansto supply air to within said support. means to conduct air fromsaidsupporttosaidbanandmeanstooseiilate saidbarlonsitudinally.

itAstohsrinstallationeom a'isingasupport in control of said valve;

having a horizontally disposed face and a contiguous upwardly inclinedsurface,

' a grate bar having side and top walls and an open bottom slidablymounted on said horizontal surface, said bar extending in the directionof said inclined surface, the end of said bar adjacent said surfacehaving a raised portio said top wall sloping downwardly from the top ofsaid raised portion to the end of said bar, a series of apertures insaid top wall, means to oscillate said.

bar longitudinally, means adjacent the other end of said bar to propelfuel toward said raised porshoulder on the portion within the hopper, an

opening in said wall extending above said bar, a slidable gate for saidopening, a fluid presure operated motor for operating said gatecomprising a cylinder having a port at either end and a third port inits side wall, a piston in said cylinder yieldably connected with saidgate, a second fluid pressure operated motor to oscillate said bar,means to conduct fluid under pressure to one of the flrst mentionedports, and means to connect the third port with said second motor.

15. A stoker installation for a furnace comprising a fuel hopperadjacent one wall of the furnace, a grate bar extending from within saidhopper to within said furnace and having a shoulder on the portionwithin the hopper, an opening in said wall extending above said bar, aslidable gate for said opening, a fluid pressure -operated motoryieldingly connected with the gate and movable between two definitelimiting positions, a second fluid pressure operated motor foroscillating said bar, means to conduct fluid under pressure to the firstof said motors and thence to said second motor, the arrangement beingsuch that the first of said motors must move to one of its limitingpositions before the fluid to the second motor.

-i8.Astructureaccordingtoclaim l4further characterized by a fluidpressure responsive valve connected with the said means to conduct fluidunder pressure to the first of said motors for reversing the directionof flow offluid throuah said motors.

1'1. A stoker installation comprising a pair of grate bars each providedwith means 'to propelsolid fuel therealong upon oscillation thereof, afluid pressure operated motor for each of said bars, a source of fluidpressure, means connecting said source with said motors whereby saidbars will move in opposite directions, means connecting said source withsaid motors whereby said bars will move in reversed opposite directions,a reversing valve determining the means connected, and fluid pressureresponsive means connected with said first and second mentioned meanscmnmcanm;

